Generally, when the resin is heated to a temperature equal to or higher than the glass transition temperature or the melting point, molecular motion thereof is highly activated so that the solid state cannot be maintained, whereby the resin is liquefied. Meanwhile, sliding members such as automotive brake components and bearings and fuel cell separators are exposed to an environment heated to 80° C. to 120° C. depending on their use conditions. Thus, in order for a resin to be used under such a condition, the resin must have heat resistance and a heat-radiation property.
One known method for imparting heat resistance to resin is a method of incorporating an inorganic filler into the resin. Through incorporation of inorganic particles into the resin, motion of resin molecules is restricted and constrained, thereby elevating the softening temperature point of the resin composition. In addition, addition of inorganic filler can improve thermal conductivity of the resin. Hitherto, ceramic powder and carbon materials (carbon particles, carbon fiber, etc.) have been employed as such fillers. Among them, carbon materials have been employed in sliding members and fuel cell separators, for their chemical inertness, high self-lubricity and high electrical conductivity.
However, carbon particles form thermal conduction paths through point-contact between particles. Therefore, in order to attain satisfactory thermal conductivity, a large amount of carbon particles must be incorporated into resin, which results in difficulty in preventing decrease in mechanical strength. On the other hand, carbon fiber, which is formed of carbon material which is difficult to graphitize and difficult to crystallize, has poor thermal conductivity and cannot fully attain shape-derived advantages. In fact, in order to attain satisfactory heat conductance (e.g., a thermal conductivity of 0.8 W/mK or more), carbon fiber must be added in an amount of 50 mass % or more, like in the case of carbon particles. Furthermore, since carbon fiber has a rigid structure, a resin composition containing carbon fiber exhibits significant shrinkage anisotropy in molding process, so that there is a problem that it is difficult to control dimensional accuracy.
In recent years, there has arisen keen demand for a heat-resistant slide bearing made of synthetic resin, which can exhibit an excellent sliding property in a high-temperature atmosphere, and some proposals have been made. For example, Japanese Patent Application Laid-Open (kokai) Nos. 2000-169738 and 2001-40225 disclose sliding members formed from a resin composition obtained by adding tetrafluoroethylene resin to polyether-ether-ketone resin which is excellent in heat resistance and mechanical strength and is widely employed in various industrial fields. Although the technique aims at improvement in the sliding property through addition of tetrafluoroethylene resin serving as a lubricant substance, wear resistance and mechanical strength remain insufficient and therefore the fact is that an additional reinforcing material such as carbon fiber or glass fiber is used to make up for the insufficiency. Such a composite material containing carbon fiber and glass fiber as additives has been employed in practice with a counter member made of steel (SUS 45). However, the composite material problematically wears the steel counter member.